What HVAC system should I use?

In most homes the HVAC energy use makes up the largest percentage of the home’s energy consumption. This information is becoming common knowledge as more individuals become energy savvy but many individuals still wonder which system is the best for them. There are various systems that can be used to heat the home but as certain system types are being phased out due to technology, such as boilers, other are beginning to rise to the top. These systems are heat pumps and furnaces. In most cases people are familiar with these systems but they may not realize which is better for them or what the differences in them are.


The first bit of information that a homeowner should understand about a system is that no matter what system is installed it should be installed properly. This is especially critical for the air conditioner. All systems must be sized and designed properly to provide quality and efficient heating and air. To start a load calculation must be performed. This is referred to as a Manual J calculation. Beyond sizing the system the ducts and registers must be sized to the system to properly provide conditioned air to the home. This is a lengthy process and for more information regarding proper installation please refer to my previous blog Why HVAC isn't just a lot of hot air .

Your system selection will depend on your climate location but here is some information about each popular system type.

1. Air Source Heat Pump: Air source heat pumps have the benefit of providing both heating and cooling function and are essentially an air conditioner that can work in reverse. Heat pumps do not create heat but rather transfer it from place to place. For this reason they are extremely efficient and can actually transfer more energy than what they consume. Air source heat pumps draw their energy from the outdoor air. Because of this they are not appropriate for areas of extreme cold. Also heat pumps can require a back up heat source for colder days. This is typically done with an electric backup. This electric back up can be extremely costly and therefore should be avoided as a heat source much as possible.

2. Hybrid Systems: A hybrid system is an air source heat pump with a gas backup. This is a good system for areas in which a heat pump is a good choice for the majority of the time but there may be short periods of extreme cold in which the backup heat strips on conventional heat pumps my run for extended period of times. Hybrids are most efficient in transition areas between warm climates and cold climates.

3. Ground Source Heat Pump: Ground source heat pumps work exactly the same as air source heat pumps but they draw their energy source from the ground. Since the ground stays at a constant temperature the heat pump is able to be more efficient. Ground source heat pumps are more expensive than air source heat pumps and extremely efficient air source pumps can come close to the same efficiency as low efficiency ground source systems. One bonus to ground source systems is many of them have the ability to heat water as well.

4. Furnaces: Furnaces are generally efficient than heat pumps but they are better in cold climates. This is due to heat pump efficiencies decreasing as the outdoor temperature decreases. Heat pumps require the use of electric heatstrips to make up for this deficiency.  Due to this furnances are a better fit in the colder climates.  In considering a furnace one must consider the climate they are in and if it is a better fit than a heat pump for their home.

5. Mini Splits: Mini splits are the same as air source heat pumps but they do not require the installation of ducts. This has several benefits especially for retrofits. Small units are placed in each conditioned space and can be individually controlled. By eliminating ducts you also eliminate the losses associated with ducts.

6. Air conditioners: There are little options available for air conditioners. If you are not using one of the heat pumps you must also install an air conditioner. If you are in a climate in which you must install an air conditioner choose one that has the highest efficiency appropriate for your area. For areas in which cooling is only needed for a few days a year an extremely high efficiency system may not be appropriate where as in areas of extreme heat the highest efficiency system will have a relatively quick payback.

Don’t turn up your thermostat more than 2 degrees at a time.

While this really only applies to heat pumps it is good information to know. By turning up the temperature more than 2 degrees the heat strips on the system will cut on. This is extremely expensive heat and will quickly run up your electric bill. If you have a programmable thermostat make sure you have one with adaptive recovery. This will prevent your system from trying to raise the temperature too much as one time and cutting the heat strips on.

How to seal your ducts

Your duct leakage can account for up to 20% of your leakage in your home. This is considerable amount in itself but is even more of a concern when you consider that in most homes the majority of the ducts are located outside of the conditioned space in the attic or crawlspace. The leakage into these spaces is costly and can create unwanted pressure differences in the home.

Locating the Leaks

The first step in eliminating the leaks in your duct work is to find them. This can be done in several ways but some are easier than others.

1. Visual inspection: All steps in finding the leaks will involve this process. You need to visually inspect the ducts to find any visible separations, penetrations or dislocations in the ducts. Some may be obvious while others may be hidden. Look for areas where duck tape may be failing (yes is it duck and no it should not be used to seal duct joints.), at locations where two ducts meet, around the boots in the floor or ceiling and at the trunk line.

2. Duct blaster: You can have a professional perform a duct blaster test on your duct work. This will let you know how much leakage is in the duct work but by itself it does not tell you where the leaks are. You can however have the professional use theatrical smoke to fog your duct work. This will allow you to see where the leaks are as the smoke will exit at the leaks.

3. Panning: Again a professional is needed for this. A professional will use a blower door and a pan to test your ducts to see which ones are leakier. This method can help isolate problem ducts but it does not have the ability to locate the leak itself.

Fixing the leaks

Once you have located the leaks you need to fix them. First you need a few supplies. These are:

1. Mastic- a material used to seal the ducts
2. Cheep paint brush-used to apply the mastic
3. Fiberglass tape-used with the mastic to seal the joints
4. Large zip ties- used to secure the inner and outer layers of the duct work
5. Duct-you may need to replace torn sections.

Duct Joints:

If you have leaks at the joints of the duct work you will need to seal these joints with mastic. This will be where the majority of your leaks are so this is the most common fix. First remove any old tape form the joint and then remove the outer layer of the duct. This is if you have a flex duct. If the inner plastic layer of your ducts is not secure you can use a zip tie to secure the inner duct. Next apply a large helping of mastic to the inner layer of the duct. You can then slip the outer layer back over the duct. Some individuals like to also secure the outer layer as well using the zip ties. You will then mastic the outer layer as well using the same technique you used on the inner layer. Make sure you pull the insulation (outer layer) over any boots or collars.

Disconnected Ducts:

If you have any fallen or disconnected duct work you will reconnect the duct work in the same manner as described in the above step.

Metal ducts:

This covers both the metal supply ducts and trunk lines. You will follow similar steps as in the duct joints section however you will use metal sheet screws to secure the duct if needed. Also you may have some gaps larger than ¼” and will need to use the fiberglass tape along with the mastic.

Torn ducts:

Unfortunately flexible duct work will tear. If this happens you may not be able to repair the duct and will need to replace the whole run or just a section. If you are repairing just a section make sure you use metal joints at both ends of the patch and use the same techniques as in the duct joint section.

Alternative methods:

There are alternative products and methods to sealing your duct work. These include mastic tape and foil tape. Mastic and mastic tape is best used on duct work but foil tape can be used to seal items that need to be routinely opened like your air handler.

There is also an alternative method of sealing that a professional can do. This involves spraying an adhesive/sealant through the duct work. The sealant finds its way into the leaks and seals anything up to a ¼”. This can be a cost effective way to seal the duct work if you have several small holes.

Don’t “crank” your dial on your thermostat.

Moving the temperature setting higher up on your thermostat does not make you home heat up any quicker. If you have a heat pump move your thermostat 2 degrees at a time to help conserve energy. If the thermostat setting is raised greatly the heat pump will use your heating strips to heat the home costing you a lot of money.

Why HVAC Isn’t Just a Lot of Hot Air (or Cold, Either)

Ever since I started my career in the construction industry, I have always seemed to run into problems with HVAC systems. This shouldn’t be that surprising, since the HVAC system is the primary system responsible for the living conditions in your home and can have the most impact on how a building functions. I have seen systems that are contaminated with fungal growth, systems that you would think had been installed to provide irrigation to the crawlspace, systems that my 8 -year-old niece and nephew could have installed, and systems that are a piece of art. However, out of all of these, the latter is the rarest of them all.

In the past year, I have dealt with systems that

• increased the gas bill after the system was installed,
  
• caused the homeowner to pay more per month than they were per season before it was installed,
  
• were not cooling or heating the home equally. The excuse for this was that two systems should have been installed, when the contractor installed only one - however, that one unit was not properly installed (twice), and ended up causing damage to the ductwork.
  

These are only three of the multitude of cases where I have seen of improperly sized, installed, or designed units. Why is this? The only explanation I can come up with is that homeowners - and unfortunately, most HVAC technicians - do not understand the impact the system can have on the home, and that it is not as simple as a fan moving air through some round tubes.

There is a standard of practice set forth in both the building code and by industry organizations that state how a system should be designed. This process takes into account how each component of the system works with the other, and combines them to provide efficient delivery of your conditioned air. This whole process starts with what is called a load calculation, or Manual J calculation. This takes into account the construction of your home and how heat is transferred between the exterior walls, ceiling, floor and the exterior environment. The next step covers the system selection or Manual S. This outlines the proper method to select a system to accommodate for the required load calculations. Next comes Manual D, which is another critical step as this is the duct design. Each system must have the ducts designed for the unit to be installed. Finally is Manual T, which is the register and grill sizing. Even grill sizes can impact your comfort levels!

Properly designed systems can increase your comfort and decrease the cost of your utilities. Next time you are going to have your HVAC system replaced, take note of these simple reminders, and hopefully, you will have your system properly installed:

1. Make sure Manual J, S, T, and D calculations were performed for your system.
Of all of these, Manual J and D are the most critical. Whether you are having your home system replaced (ducts and system) or just the unit, these calculations are critical. There is no such thing as rules of thumb or matching the system with what you previously had. Each home is unique, and the system you had before may have been improperly sized.

2. Your ducts impact your system’s efficiency.
While most people will try to just install a new unit and keep using the old duct work, this can actually cost you money. If ducts are improperly sized for the system, they can cause the system to operate inefficiently. Why pay for the more efficient system if it is going to operate at a lower efficiency than the one you just replaced?

3. Manual J has safety factors already figured in.
There are some companies that will perform Manual J calculations, but they will not use the weather data provided in the back. Instead, they will design the system for hotter temperatures. You don't design systems for newsworthy days! By raising the design temperature, you oversize the system. When you do this, you size the system for 1% of time it is in operation - and oversizing for 99% of the time.

4. The lowest or highest price may not be the best.
It's hard to judge an install on just the price of the system. HVAC installs can vary greatly! ACCA (Air Conditioning Contractors of America) has produced a document that allows you to compare bids so that you get the best value. However, remember that if the contractor doesn’t properly design the system, it doesn’t matter how good their price is! You can get the document here: Quality Installation Specifications

Do NOT Install Replacement Windows!

The tip this week is more of a what not to do instead of a what to do. Every day, I see a commercial advertising replacement windows and how much money they can save you; and every day, I know someone has invested a lot of money into their home that they will not get paid back.

Many people are advertising 50% savings with the replacement of new windows. This is completely true. You may save 50% on the amount of energy the windows cost you, but this translates to only about 10% to 15% of your total bill. With this limited savings as compared to the cost of the windows, you end up with a very long payback period. If 10 windows cost you between $6000 and $7000 and you save a gratuitous 20% on a utility bill of $200, your payback will be between 12 and 15 years. This is almost a best-case scenario. In most cases, the paybacks for replacement windows are going to be between 20 and 30 years, because the savings will not be that great for such a small investment.

Most homeowners are not going to be in the home for 15 years, and if they are, there are several other items that can be done to the home that have a quicker payback. I will only recommend replacement windows in extreme cases. In the majority of the homes I see, I would more likely recommend installation of storm windows (for single panes), or repair of the windows currently in place, typically because those are the best scenarios when windows are involved. So next time you have someone suggest you replace your windows or you see the commercials, remember that those windows will save you money, you are better off investing in other, similarly effective improvements that have a much shorter payback period.